Breech-loading magazine firearm



Aug. 10, 1954 L. R.' CRITTENDON ET AL BREECH-LOADING MAGAZINE FIREARM Filed Sept. l2, 1951 '3 Sheets-Sheet l Eri@ am. Hamann? b l? BY w/UAM @f1/L5M.

A. ATTORNEYS Aug. 140, v1954 L, R. CRITTENDON ET AL v BREECH-LOADING MAGAZINE FIREARM l f Filed sept. 12J 1951 FII@ ----z.------T--------:----------:n:

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A TTONEYS Aug. 10, 1954 R. cRlTTENDoN ET AL BREECH-LOADING MAGAZINE FIREARM 3 Sheets-Sheet 5 Filed Sept. l2, 1951 rllx E" n m OM w/L H. BY /A/V GIA L J A TTOHNE;

Patented Aug. 10, 1954 BREECH-LOADING MAGAZINE FIREARM Lexie Ray Crittendon an N. Y., assignors to Rem Inc., Bridgeport, Conn.,

Walle d William Gail, Jr., Ilion, ington Arms Company, a corporation of Dela- Application September 12, 1951, Serial No. 246,306

12 Claims. l

This invention relates to a breech loading magazine firearm and has particular reference to an arm of that type in which the breech closing bolt has a rotary motion to and from locked position and a reciprocatory motion after unlocking to expose the breech of the barrel. The invention is applicable to either manual actuation, as by a fore-end slide; or to autoloading actuation, as by a reciprocable, gas and/or recoil operated, member.

The prior art firearms of the types to which this invention is applicable have, without exception, been quite expensive to manufacture, and in order to provide adequate strength, have required such ycare in selection of materials and design of components that only one manufacturer has been able to manufacture them for use with the highpowered sporting rifle cartridges. Further, not all of the designs previously available resulted in the smooth, streamlined appearance so desirable to the connoisseur of fine firearms.

The major objects of this invention were the production of firearms of the types mentioned above which could be manufactured with great economy, which were adaptable to, and safe with, the highest powered sporting and/or military ammunition, and which posessed an appearance superior to that of any of the prior art arms of these types.

In achieving these objects, we found it desirable 1 to employ for both arms the greatest number of identical components possible and to make the greatest possible utilization of component parts from other firearms of current manufacture.

We have effected a very high degree of interchangeability of parts between the autoloading and slide actuated versions of our new rifle and have used almost, without change, the fire control assembly which is the subject of the lco-pending patent application of Lexie Ray Crittendon, Serial No. 204,706, nled January 6, 1951, now Patent No. 2,675,638, which is a continuation-impart of the copending application of the same inventor, Serial No. 79,368, filed March 3, 1949, now Patent No. 2,570,772. In this way, any single part requires the production of a suiiiciently large number of units to justify the most efficient production tooling. Without this marked family resemblance, the quantities of each individual part might not justify manufacture by other than modified j ob shop methods.

The exact nature of the invention as Well as other objects and advantages thereof will become more clearly apparent from Consideration o f the following specification referring to the attached drawings, in which:

Fig. l is a longitudinal vertical sectional View through an autoloading firearm embodying our invention. The mechanism is in breech closed position with the hammer cocked.

Fig. 2 is a view similar to Fig. l, with the mechanism in the breech open position.

Fig. 3 is a side elevational View of the bolt utilized in these rifles.

Fig. 4 is a front elevational view of the bolt shown in Fig. 3.

Fig. 5 is a side elevational view of the bolt carrier.

Fig. 6 is a side elevational view of the rear portion of the assembly of barrel, barrel bracket, and barrel extension.

Fig. 7 is a partial side elevational View of an assembled autoloading rifle embodying our invention.

Fig. 8 is a partial vertical sectional View on the line 8 3 of Fig. l.

Fig. 9 is a partial vertical sectional view on the line 9 9 of Fig. l.

Fig. 10 is a partial vertical sectional view on the line ill-IG of Fig. l.

Fig. 11 is a partial vertical sectional View on the line H-il of Fig. l.

Fig. 12 is a partial horizontal cross-sectional View on the line IZ-I 2 of Fig. l.

Fig. 13 is a view similar to Fig. l, showing the application of our invention to a forearm slide operated rile.

Fig. 14 is a partial side elevational View of the sub-assembly of barrel, breech bolt and breech bolt carrier in breech locked position.

Referring to the drawings by characters of reference, it may be seen that the autoloading embodiment of our invention comprises a receiver l, and a barrel 2 provided with a barrel bracket 3 which has a force fit on the chambered end of the barrel. The barrel is also provided with a barrel extension 4 threaded on the end of the barrel per se and assisting in the retention of the barrel bracket, both barrel extension and barrel bracket reinforcing the chambered portion of the barrel which is subjected to high internal pressure when the cartridge is fired. The barrel extension is arranged to pass into the receiver through the front end thereof and the rear face of the barrel bracket is clamped against the matching forward face of the receiver by a bolt 5 cooperating with a partially split jam nut 6 engaged in a conical counterbore l in the barrel bracket face.

In the top and two side walls of the receiver We have provided three guide grooves 3, each of these grooves mating with a complemental guide rib Si on a breech bolt carrier An axial bore is provided in the bolt carrier to receive porti n il of the breech bolt l2, wherein one or more cam grooves, each comprising a helical por merging into a straight portion Ed, are ded. These cam grooves are each arranged to receive a cam pin i5 mounted in the carrier con-- veniently in one or more of the thicker portions thereof provided by the guide ribs 9. In the gasoperated embodiment of our vention, it is con venient to form the breech operating handle iii an extension of one of the pins.

It should be obvious that the earn pin and groove connection between the carrier and bolt provides for relative rotation of members as a function of relative axial movement beta-'een them. This relative rotation is utilized to loci: the breech bolt to the bar el extension throin i the agency of interrupted thread loelting lugs on the bolt head and complemental looking abri; ments i3 in the barrel extension. With the ce o pins in the straight portion lil of the groo r e locking lugs are in locking engagement f ith each other and after relative reciprocation has placed. the cam pins in the remote end of the helical portions i3 of the grooves, the bolt head will have been rotated to a position in which the locking lugs il and the interruptions therein will line up respectively with the interruptions in abutments i8 and the solid portions of the abutments le. Thus, the bolt carrier and the bolt head will be free to reciprocate together relative to the barrel extension and the receiver after the c-.arc pins have been moved to the rear end of the helin cal portion of the cam grooves.

To insure that the correct alignment will be maintained during reciprocation of the bolt bolt carrier, the interruptions in the barrel extension locking abutments le preferably are arranged to form continuations of the receiver guide grooves 3. Thus, when the breech bolt has been rotated to unlocked position, one or more of the bolt locking lugs will be guided in reoiprocation by the guide grooves in the receiver.

By comparison of Figs. 1, 3, e, and 9. it will be noted that Figs. 3 and e show the bolt in the posi.- tion it occupies in the rifie when the breech locked and it will be noted that in this position one of the interruptions between the locking lugs il is substantially lined up with the position occupied by the right hand guide rib e on the bolt carrier lil. As a safety feature, this guide rib is carried forwardly beyond the body of the bolt carrier to form a key i9.

In the very remote event that the ride in advertently assembled Without the com pins in place, or in the still more remote event that the cam pins or earn grooves both failed sirriultaneM ously, it would be possible to seat the bolt in the barrel extension without rotating the bolt to engage the respective locking lugs. This would ce a very dangerous condition. and is the primary reason for the provision of the key itl. 'it 'will be noted that with the bolt in any other position of rotation. than one in which the locking lugs in full mutual engagement, the key i8 will the rear end surface of one of the sets of bolt locking lugs before the carrier can move forward relative to the bolt body to seat against the shoulders formed on the body thereof. Since other safety features to be later described are dependent upon the position of the bolt carrier rela- 4 tive to the bolt body, this use of the key i9 prevents firing from an unlocked bolt.

To provide a force for primary extraction and initial chambering of the cartridges, the locking lugs are preferably cut as helical threads of moderate pitch. This pitch is flat enough that under most conditions of lubrication these threads Will lock while the high breech pressure is effective. However, there is a theoretical di. advantage in that a component of the gas pressure in an exploding cartridge tends to rotate the breech bolt head to its unlocked position. The body iSd of the key i9 also overcomes this ti ical disadvantage, as will be described. Through the cam pins in the straight portion le of the cam grooves, the bolt rotating component of breech pressure is transmitted to the bolt carrier and will be resisted by the inter-engagement of the guide grooves s and guide ribs e. This arrangement has ordinarily been considered adequate in the relatively heavy constructions of the prior art which use generally similar breech loci.n ing arrangements. In our construction, however, vie prefer to eliminate any possibility of applying explosion pressure loads to the receiver, permit ting a lighter, more economical receiver design. rIhe body i901, of the key le on the boit carrie-r aids in this result since, in the completely locked breech position of the carrier, the key le and at least a portion of the body ma is engaged in a recess 2e in the barrel extension. Thus, the bolt rotating component of the explosion pressure is transferred back to the barrel extension v hie is necessarily a very strong member which can conveniently and economically be formed of high strength, heat treated Steel. Since this carrier rotating force component exists only during the explosion of the powder in the cartridge, it will act in only one direction, tending with the arrangement shown to rotate the bolt carrier clockwise, as viewed from the rear and, hence, it is only necessary to lit a corner of the body for engagement with a single upwardly facing surface 2l on the barrel extension. The surface 2l is most conveniently one edge of the recess 2i? which has the additional function of providing clearance for the ejected shells and lines up with the end of the ejection port in the receiver.

In addition to the two safety functions just described, the over-travel of the carrier in the straight portion of the earn grooves has tivo other important safety functions. in the first place, the ring pin 22 is secured to the carrier with only limited freedom for reciprocation. In position other than that in which the cam pins are in the foremost end of the straight part of the cam grooves, the firing pin Will not protrude from the bolt face far enough to fire a cartridge. A second function of this straight portion 's to provide a slight time delay between the initiation of carrier movement in an autoloading firearm and the commencement of the unlocking action. By suitable choice of the position of the gas operating member and the length of the straight portion of the grooves, this time delay may be made more than adequate to permit the bullet to leave the barrel and residual gas pressure to drop to a safe level before unlocking is started.

A further function of the straight portion of the grooves is to permit a substantial amount of kinetic energy to be developed by the carrier in either a manually or automatically operated firearm and thus provide an impact Wrench effect in starting rotation of the breech bolt to unlocked position. Particularly with modern cartridges developing very high gas pressure, this eiect, in conjunction with the pitch of the locking lug surfaces, is quite helpful in primary extraction or the loosening of the cartridge case from the chamber walls.

From an inspection or Figs. 3 and 4, it may be noted that we have employed a minor modification of the extractor-bolt head arrangement which is the subject of the patent to Howell, No. 2,423,373, granted June 14, *1949; This modification consists in rigidly fastening one end of the ring extractor 23 to the bolt flange 2s as by a rivet 25. As in the co-pending application of Merle H. Walker, Serial Number 69,968, filed January 8, 1949, now Patent No. 2,585,195, the circumferenm tially continuous bolt flange is received in a circumferentially continuous recess in the breech end of the barrel. In this way we have secured the practically blow-up proof construction which characterizes arms formed to' so completely en close and support the cartridge head. As in these prior constructions, we have employed a spring-urged plunger ejector 25 which functions without requiring any interruption oi the continuity of the bolt flange or barrel breech face.

The breech bolt assembly of bolt and carrier is caused to reciprocate in the receiver guide grooves 8 by means of a pair of action bars 2i which are preferably formed integrally and include a connecting yoke section 2id shaped to conform roughly to, and to be slidable within, the upper portion of the receiver l. The action bars are each slidably received in a longitudinal guide groove 2S in the receiver side walls and pass out through the front wall of the receiver in cuts 29 intersecting the opening in that front Wall for the reception of the barrel extension fi.

The rear end of the breech bolt carrier has a necked down portion 312 formed to be received within the yoke 21d joining the action bars, as best seen by reference to Figs. l, 2, and 11. To provide a better support for the right hand side of the carrier, Where a portion of the right hand receiver guide track 8 is cut away to form the ejection port, a tab di on the right hand action bar is provided to engage beneath the right hand guide rib 9 on the carrier. ln this way, the guide groove 28 and the action bar participate in the support of the bolt carrier. This arrangement also functions to positively prevent any upward displacement of the action bar yoke relative to the necked down portion of the carrier. if desired, the action bar yoke 2id may be permanently secured to the necked down portion fie of the bolt carrier by any such convenient means as a furnace brazing operation.

The assembly of action bars, carrier, and bolt, may be inserted into or removed from the re ceiver as a unit through the opening in the front end of the receiver. When assembled, they are retained in place by the assembly of barrel extension, barrel, and barrel bracket mounted on the receiver with the barrel and barrel extension extending into the receiver. The portion of mechanism thus far described is not materially different in the gas operated autoloading arm and in the slide actuated arm which is illustrated in Fig. 13.

The appearance of either arm and its resistance to the penetration of dust and other foreign objects is improved by the use of an ejection port cover such as 32 which may be fitted to slide in grooves in the receiver as shown in the crosssectional views Figs. 9, l0, and l2. Preferably, the cover is arranged to have a limited degree of lost motion relative to the breech bolt carrier by which it is most conveniently operated.

A similar cover is provided for the manually operated arm shown in Fig. 13 and in either case the cover is, as shown in Fig. l2, moved back and forth by means of lugs 36 extending inwardly from the face of the cover a distance sufficient to be engaged by opposite end faces 37 of the right hand carrier guide rib 9. Obviously, these covers may be assembled in the firearm by placing the central portion of the cover in engagement with the outer surface of the right hand carrier guide rib and then sliding the assembly of action bars, carrier, bolt, and ejection port cover rearwardly into the receiver through the open front end thereof.

As may be seen by reference to Figs. 7, l0, and l2, the ejection port cover has, in the gas-operated riiie, the additional function of retaining in place the manual operating handle EE. To perform this function, the cover 32 is formed to define a slot 33 which, for the major portion of its length, is of barely suiicient width to pass the necked-down portion of the handle l and of insuicient width to pass the cam pin portion i5 of the handle. Assembly and disassembly are made possible by providing in an intermediate position in the slot 33 an enlargement 34' of sufficient size to pass the cam pin portion i5. Thus, after the cover and bolt assembly have been inserted into the receiver as described in the preceding paragraph, the ejection port cover may be positioned to align the enlarged portion 3d with the cam pin bore in the carrier and the handle inserted. At either extreme position of the bolt, the handle will be retained by the narrower portion of the slot. In normal operation, the handle will pass by the enlarged portion 34 so quickly that there will be no opportunity for disassembly, and no other detent means is shown or ordinarily necessary. The side of the receiver is slotted at 35 to provide clearance for the handle i5 during the full rearward travel of the operating handle in normal gun operation.

Obviously, in the manually operated ride shown in Fig. 13, all operation of the bolt is by the grip 1d; hence, the handle i6 is unnecessary as are the slots 33 and 35.

Each form of the rifle employs a fire control mechanism which is essentially that disclosed in the copending Crittendon application, Serial No. 204,706, previously referred to. To minimize the need for reference to that application, it may be noted here that the entire mechanism is mounted on a trigger plate 38 which is inserted between the side walls of the receiver and held in place by a pair of detent retained trigger plate pins 3d. The trigger plate has mounted on it a hammer fill urged by a spring ll! and plunger l2 to swing toward the firing pin 22. A pivoted Sear i3 is urged by a spring @d in a direction to engage and retain the hammer and may be moved by a trigger and connector t to hammer releasing position. The connector c5, it will be noted, has a releasable engagement with a step 47 on the sear and is provided with a forn wardly extending arm 48 which is engaged over a pivotally mounted disconnector 59. .actuation of the disconnector may be either the result ci the action of the hammer spring plunger i2 on the short arm 50 of the disconnector as the hammer falls or the over-riding of the long arm 5i of the disconnector by the action bar when the breech bolt carrier is moved rearwardly from locked position. In either case, the connector will be disengaged from the sear and it will be impossible for the sear to be released by the trigger until the trigger has been completely released and the disconnector restored to normal position. This arrangement prevents full automatic firing or the firing of repeated shots with only one pull of the trigger and it prevents firing whenever the breech is not securely locked. The usual type of cross bolt safety 52 is provided to lock the trigger for safe carrying of the loaded rie.

In the manually actuated riiie shown in Fig. 13, essentially the same mechanism is utilized. The long arm of the disconnector in this rifle is identified by the numeral 53 and is formed to engage with the action bar in a positive connection. The disconnector then functions as an action bar lock to prevent the shooters normal rearward draft on the fore-end from opening the action until the rifle has been fired and the action bar lock released by the fall of the hammer and action of the hammer spring plunger on the short arm Sil of the combined disconnectcr and action bar lock. To permit unlocking of the action without firing, a finger piece "ce is formed on the disconnector and extends downwardly through a slot in the trigger plate, where it may be engaged and operated manually. When a shooter is exerting the normal rearward draft n the fore-end, hangre protection is provided by frictional forces acting on the end of the arm 53 which will prevent release of the action bar lock on fall of the hammer until the shooters rearward draft has been released consciously or involuntarily as the rie recoils in his grasp.

In either form of the rifle, the same conventional type of box magazine 55 is received in the recess defined by the front and side walls of the receiver and by the front end of the trigger plate. The magazine is retained in this well by the engagement of a lug with a recess S in the receiver wall and by engagement of a spring-urged magazine latch 5'! on the trigger plate with an opening 58 in the rear wall of the magazine box.

It will be seen that in respect to the essentials of a working center'lre rifle, both modifications illustrated are essentially the same and that substantially identical breech mechanism is actuated in either case by a pair of reciprocating action bars extending through the front wall of the receiver in general parallelism with the bore of the barrel.

In the gas operated semi-automatic modification, the front ends of the action bars are riveted or otherwise secured to a sleeve 59 which is supported for reciprocation on an action tube Se. rlhe action tube 60 is supported at the rear end by engagement over a reduced diameter portion of the barrel bracket bolt 5 and within a counterbore in the jam nut E. Frontal support for the action tube is provided by engagement in a bore in the support plate 5i which is secured to the barrel lug 52 made integral with or secured to the barrel. An action spring 53 is confined on the action tube between the jam nut 5 and a rearwardly facing surface in the sleeve 5S, tending at all times to move the sleeve and breech mechanism to their foremost positions.

The sleeve is driven rearwardly each time the riiie is fired by a portion of the propellant powder gas tapped off through a gas port and led rearwardly through gas tube 64 into a blind hole or gas cylinder 65 in the sleeve 59. The gas tube has a very loose fit in the cylinder providing an annular space around the gas tube through which the gas can escape forwardly. The gas therefore acts both by impulse and reaction in starting the rearward motion of the sleeve which is continued by the inertia of the parts after the sleeve clears the end of the gas tube. Arranged in this way the gas port, gas tube, and gas cylinder blow themselves clear at each shot and cleaning is seldom necessary. For inspection of the gas port, the screw 56 may be readily removed and the gas tube and gas cylinder are both conveniently accessible when the breech mechanism is held in its rearmost position.

A wooden fore-end 61 is provided with a metal sleeve liner 68 and secured around the action tube and sleeve by engagement between the front face of the receiver and a takedown screw 99 threaded into the barrel lug 52. This fore-end provides a convenient hand grip and guards the hand from the moving sleeve and from escaping gas. Although, as has been noted previously, the gas system is opened up after a short rearward movement of the sleeve, such movement does not commence until after the bullet has left the barrel and the gas tube is not completely open to atmosphere until the residual gas pressure has fallen to a relatively low value. Such gas as continues to flow through the gas tube is at such low pressure and temperature that it escapes harmlessly through the space between the fore-end and the barrel. Gas escaping through the annular space between the gas tube and gas cylinder, although initially of higher pressure and temperature, dissipates most of its energy in work upon the sleeve and hence, it also may be permitted to escape harmlessly.

It may be emphasized here that the action tube 6B is not rigidly secured to the barrel at either end. Consequently, as the barrel heats up and expands, there will not be any differential expansion force acting to bend the barrel and change the point of impact, a diiculty which has been all too common in gas-operated autoloading arms.

'Ihe manually operated rifle shown in Fig. 13 is provided with an action tube 'lil which is brazed or otherwise secured to a barrel bracket nut il preferably provided with a fiber locking insert of the type shown, for example, in United States Patent No. 1,729,013, or No. 1,550,282. When the barrel bracket nut is tightly fastened, the action tube forms a rigid support axially parallel to but structurally inde pendent of the barrel. Upon this action tube an action sleeve 72 is slidably mounted and provided with a collar 13 to which the action bars are riveted or otherwise secured.

Mounted on the action sleeve is the usual wooden grip 'lli of a slide action firearm which is retained in place by the grip nut l5. The forward end of the action tube is closed by a plug 16 which provides a denite stop for the grip and which provides a base for mounting a spacer 11. The spacer is curved to conform to the lower surface of the barrel and thereby pre vents twigs or grass from entering the space between barrel and action tube if the rifle should be carried for any distance with the breech open. This spacer, however, is not fastened to the barrel in any way and it is preferably rotatable on the plug T6. The use of the spacer does not therefore interfere with the free floating character of the barrel or tend to modify the shooting characteristics of the rie as a function of the grip of the shooter upon the fore-end.

Although we have shown and described fairly specically only two embodiments including our invention, we wish it to be understood that We do not consider our invention to be limited to the specic constructions shown. For an exact definition of the limits to be placed upon our invention, reference may be made to the appended claims.

We claim:

l. In a iirearin having a receiver, a reciprocating breech bolt carrier housed and guided within said receiver, and a breech bolt coupled to said carrier, the combination comprising means defining a recess in the upper portion of said carrier; a pair of action bars extending out of said receiver and guided for reciprocation in said receiver; and a yoke portion joining the rear ends of said action bars and passing through said recess in the carrier, whereby reciprocation of said action bars will cause reciprocation of said carrier.

2. In a firearm having a receiver, a reciprocating breech bolt carrier housed and guided within said receiver, and a breech bolt coupled to said carrier, the combination comprising means defining a neck of reduced cross-sectional area on said carrier; a pair of action bars extending out of said receiver and guided for reciprocation in said receiver; and a yoke section integrally joining the ends of said action bars within the receiver, said yoke section embracing said neck on the carrier to constrain said carrier and action bars to reciprocate together.

3. In a firearm having a barrel, a receiver, a reciprocating breech bolt carrier housed and guided within said receiver, and a rotating breech bolt helically coupled to said carrier, the combination comprising means defining a neck of reduced cross-sectional area on said carrier, an action bar assembly comprising a yoke embracing said neck and joined integrally to a pair of spaced-apart action bars guided for reciprocation in said receiver along paths parallel to that of said carrier, said bars extending forwardly to a position outside said receiver, and reciprocable operating means outside of said receiver coupled to both of said action bars.

4. In a irearm having a receiver formed to deiine carrier guide tracks and a breech bolt carrier formed with guide ribs slidable in said guide tracks, the combination comprising action bar guide tracks formed in opposite walls of the receiver beneath and parallel to said carrier guide tracks, a pair of action bars reciprocably received in said action bar guide tracks, a yoke integral with said action bars extending upwardly over the top of said carrier and embracing said carrier to constrain the carrier to reciprocate with the action bars, and at least one tab on the action bar extending upwardly into engagement with the lower face of one of the carrier guide ribs to assist in supporting the carrier from the action bar guide tracks and to prevent upward displacement of said yoke relative to the carrier.

5. In a firearm having a barrel, a receiver, a reciprocating breech bolt carrier housed and guided within said receiver, and a rotating breech bolt helically coupled to said carrier, the combination comprising an action tube supported by the receiver and extending forwardly therefrom in substantial parallelism with the barrel; an operating member reciprocable on said action tube; a pair of reciprocable action bars attached to the operating member and extending rearwardly therefrom into said receiver; yoke means integrally joining the ends of said action bars within the Il() receiver; and means dening a recess in said breech bolt carrier interengaging with said yoke to constrain said carrier to reciprocate with said action bars.

6. In a firearm having a barrel, a receiver, a reciprocating breech bolt carrier housed and guided within said receiver, and a rotating breech bolt helically coupled to said carrier, the combination comprising an action tube extending forwardly from the receiver in substantial 'parallelism with the barrel and supported at least in part by a bolt passing through the forward wall of the receiver, an operating member slidable longitudinally on said action tube, a pair of reciprocable action bars attached to said operating member and passing rearwardly therefrom into said receiver, means integral with both of said action bars formed to denne a single connecting yoke between said bars, and means defining on said bolt carrier a neck of reduced cross-section area relative to the portions of the carrier forward and rearward of said neck, said neck being embraced by said yoke to constrain the action bars and carrier to reciprocate with each other.

'7. The combination described in claim 6, said action bars and said yoke consisting of a single continuous metal strip.

S. In a iirearm the combination comprising a barrel provided with means formed to deiine r0 tationally separated forwardly facing locking abuments, a rotary breech bolt provided with rearwardly facing locking lugs racially engageable with said locking abutments; a reciprocating non-rotary bolt carrier helically connected to said bolt; and a forwardly extending key on said carrier which will engage with the rear face ci; one oi said locking lugs and block further movement of the carrier if said breech bolt does not rotate to place said locking lugs in engagement with said locking abutments.

i?. In a firearm the combination comprising a barrel provided with means formed to define at least one forwardly facing locking abutment and at least one rearwardly opening longitudinally ext-ending recess; a rotary breech bolt provided at least one rearwardly facing locking lug facially engageable with said locking abutment in the barrel means; and a reciprocating, nonrotary breech bolt carrier helically connected to said breech bolt and provided with a key extending longitudinally forward and engageable in said rearwardly opening recess to positively prevent relative rotation between said carrier and said barrel when the breech bolt locking lug is in engagement with said looking abutment.

l0. The combination described in claim 9, said locking abutinents and said locking lugs being formed as complemental segments of spirally arranged threads whereby a component of axial pressure exerted on the face of said bolt will tend to rotate the bolt, the helical connection between bolt and carrier being arranged to transmit said component to the bolt carrier whereby said component will be resisted by the interengagement of said key and said recess.

il. The combination described in claim l0, the helical connection between the breech bolt and the breech bolt carrier being constructed with a straight forward portion permitting relative forward movement of the carrier without rotary movement of the bolt after said bolt locking lug is in engagement with said barrel locking abutment, said relative forward movement being utilized to seat said key in said recess.

12. The combination described in claim 1l,

said key being arranged to engage said bolt locking lug if said bolt has failed to rotate into engagement with said barrel locking abutment and prevent said relative forward movement.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,316,510 Rosebush Sept. 16, 1919 1,373,888 Johnson Apr. 5, 1921 1,404,040 Mader Jan. 17, 1922 Number 10 Number 

